Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance		$ (2)	$ 245
Other comprehensive income before reclassifications		50	(246)
Amounts reclassified from accumulated other comprehensive income		0	(1)
Accumulated other comprehensive income (loss), Ending Balance		48	(2)
Pension and Retiree Health and Welfare Benefit Items [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	[1]	0	251
Other comprehensive income before reclassifications	[1]	50	(250)
Amounts reclassified from accumulated other comprehensive income	[1]	0	(1)
Accumulated other comprehensive income (loss), Ending Balance	[1]	50	0
Equity Method Investments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance		(2)	(6)
Other comprehensive income before reclassifications		0	4
Amounts reclassified from accumulated other comprehensive income		0	0
Accumulated other comprehensive income (loss), Ending Balance		$ (2)	$ (2)

[1] Amounts are net of tax. See Note 13 for additional details.